Constant tcp retransmission wireshark software#
These counters are another good software "port" of call when suspecting EtherNet/IP communications issues. I would look to the 1756-ENBT and Stratix 5700 EtherNet Media Counters, which you can access via their built-in web browser. There are retransmissions in both directions. This suggests that the PCCC command requests are not exchanging OK between the L71 and the Stratix 5700. Note: Unknown Service (0x4b) = Execute PCCC Service (SLC Typed Read/Write)ĬIP¦117¦PCCC > = Failed?.ĬIP¦117¦PCCC > = Retransmission.SuccessĬIP¦121¦PCCC > = Retransmission.Success What I believe we are looking at here is the traffic through the switch ports. Here's the capture from the port going to the L71: Here's the capture from the port going to the ML1400: Is there anyone more knowledgeable than I able to shed some light on what I'm seeing? Filtering for all other devices shows no such thing.
If we had a cabling problem on the port going to the L71, I'd expect to see that sort of symptom - but I'd expect to see it on all devices, or at least, more than one. But I'd expect to see that symptom on the port going to the micrologix, not the port going to the L71. If we had a cabling problem from the stratix to the micrologix, I'd expect to see that sort of symptom - try to transmit, receive no response, try again. This whole time, the comms was working just fine, but retransmissions abound! When I did that, every single entry was followed by a retransmission. The port going to the L71 looked OK until I filtered it for traffic to/from the problem ML1400 only. I'm very inexperienced with wireshark, so I'm definitely not able to be certain, but everything looked OK. The port going to the ML1400 seemed normal. I connected my laptop to the stratix as shown, and set it to port mirror the port going to the ML1400, and then the port going to the L71. I re-patched the network as drawn above, and everything worked (as I mentioned, it was an intermittent problem). I finally got an opportunity to go out there and do some proper diagnostics. That worked, and they've been running like that for about a month.
Constant tcp retransmission wireshark Patch#
It got worse and worse until I eventually had them disconnect the uplink between the Stratix 5700 and the unmanaged switch in the ML1400 cabinet, and string a patch cable directly between the two unmanaged switches, just to get them out of immediate trouble. There seemed to be the occasional dropout to the other ML1400 (not shown) as well, but none to the PLC's on produced/consumed, and the ML1400 in the picture was definitely the main culprit. The ML1400 doesn't talk to anything else.Ībout 4 months ago, they started getting sporadic comms dropouts between the L71 and the ML1400. The L71 also talks to one other ML1400 with more or less identical architecture, and about 5-6 CompactLogix/ControlLogix PLC's using produced/consumed tags, again with similar physical infrastructure. It's been in place and working fine for about 4 years. The L71 uses explicit messaging to read and write to and from the ML1400. Got a customer with a control system architecture like this:
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